Portable electronic devices with text entry capabilities are increasing in usage. Cellular phones, for example, have a number of features that require a user to input alphanumeric characters. A user may, for example, enter alphanumeric text in the name field of a phone list maintained in the phone. A user may also use a cell phone to send text messages via short message service (SMS) technology. To do this, a user generally inputs alphanumeric characters into the phone. Typically, a numeric keypad is used to enter alphanumeric characters, where the number of alphanumeric characters exceeds the number of numeric input keys. Keys on the keypad are typically single-pole, single-throw spring-loaded pushbutton switches that remain in a neutral (non-activated) position until momentarily depressed into an activated position.
A technique generally used to enter alphanumeric characters into a telephone uses a standard alphabetic arrangement illustrated on the cellular telephone illustrated in FIG. 1. A cellular phone typically has two data entry modes, a numeric mode and an alphanumeric mode. In the “normal telephone dialing” or “numeric” mode, activation of the data entry keys represents numeric digits. The numeric digits are determined from the correspondence between each data entry key and the numeric digit associated with that key. In a standard telephone, activation of data entry keys in numeric mode generates dual tone multifrequency (DTMF) signals in accordance with an industry standard.
In a known technique, when operating in the alphanumeric mode, single activation of a data entry key is interpreted as a user selection of the first letter in the sequence of letters that are assigned to the particular data entry key. Similarly, when a data entry key is activated twice by a user, this is interpreted as a selection of the second letter in the sequence of letters associated with that particular data entry key. Activation of the data entry key three and four times, respectively, by a user, is interpreted as selection of the third and fourth letters, respectively. Entry of the number as a numerical character is performed by activating the key either four or five times (five times for the “7” and “9” keys that have four letters thereon; and four times for the remaining numbers).
FIG. 2 depicts a key map 215 of such a conventional approach to alphanumeric data entry that illustrates required key activation, when operating in alphanumeric mode. Thus, for example, one activation of the input key corresponding to the number “2” results in a selection of the letter “A”, two activations of the input key corresponding to the number “2” results in a selection of the letter “B”, three activations of the input key corresponding to the number “2” results in a selection of the letter “C”, and four activations of the input key corresponding to the number “2” results in a selection of the numeric digit “2”.
A timeout threshold is typically used to determine when selection of a character is complete. If a period of time equal to the timeout threshold follows the activation of a key without a subsequent activation of a key, the selection of the character is considered to be completed. Also, if the user activates a first key followed by an activation of a different key, the activation of the second key is considered to be the beginning of the selection of a new character.
With this method, a user may activate a key one, two, three, four or five times in order to select a particular letter of the alphabet. Multiple activations of keys increase the time required to enter text using the keypad.
Because entry of alphanumeric characters on a limited keypad is less efficient than on a full sized keyboard, a mechanism for improving both accuracy and efficiency is desirable.